Much of our present understanding of sensory processing, particularly in the visual system, has been gained from an understanding of the anatomical connections between cells at successive levels of the nervous system and comparisons of their receptive field properties. Far less is known about the organization of motor systems from level-to- level or about the pathways and mechanisms by which sensory information guides motor activity. My long term goal is to understand the functional and structural organization of the oculomotor system and the ways in which it is controlled by the visual apparatus. I am appoaching the problem in the cat by studying the superior colliculus, the primary structure interposed between the retina and the oculomotor neurons. The synaptic organization of the colliculus will be examined with Golgi and Nauta methods, and with the electron microscope. Particular attention will be paid to the patterns of termination of collicular afferents, the intrinsic organization of the colliculus, and the detailed distribution of its efferents to the brainstem. Extracellular recordings will be made from neurons in the brainstem identified anatomically as receiving collicular input and their visual and motor properties will be studied.